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/*
* Copyright (C) 2019 Alyssa Rosenzweig
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
/* On some hardware (particularly, all current versions of Mali GPUs),
* vertex shaders do not output gl_Position in world-space. Instead, they
* output gl_Position in transformed screen space via the "pseudo"
* position varying. Thus, this pass finds writes to gl_Position and
* changes them to transformed writes, still to gl_Position. The
* outputted screen space is still written back to VARYING_SLOT_POS,
* which is semantically ambiguous but nevertheless a good match for
* Gallium/NIR/Mali.
*
* Implements coordinate transformation as defined in section 12.5
* "Coordinate Transformation" of the OpenGL ES 3.2 full specification.
*
* This pass must run before lower_vars/lower_io such that derefs are
* still in place.
*/
#include "nir/nir.h"
#include "nir/nir_builder.h"
void
nir_lower_viewport_transform(nir_shader *shader)
{
assert(shader->info.stage == MESA_SHADER_VERTEX);
nir_foreach_function(func, shader) {
nir_foreach_block(block, func->impl) {
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
if (intr->intrinsic != nir_intrinsic_store_deref)
continue;
nir_variable *var = nir_intrinsic_get_var(intr, 0);
if (var->data.mode != nir_var_shader_out ||
var->data.location != VARYING_SLOT_POS)
continue;
nir_builder b;
nir_builder_init(&b, func->impl);
b.cursor = nir_before_instr(instr);
/* Grab the source and viewport */
nir_ssa_def *input_point = nir_ssa_for_src(&b, intr->src[1], 4);
nir_ssa_def *scale = nir_load_viewport_scale(&b);
nir_ssa_def *offset = nir_load_viewport_offset(&b);
/* World space to normalised device coordinates to screen space */
nir_ssa_def *w_recip = nir_frcp(&b, nir_channel(&b, input_point, 3));
nir_ssa_def *ndc_point = nir_fmul(&b,
nir_channels(&b, input_point, 0x7), w_recip);
nir_ssa_def *screen = nir_fadd(&b,
nir_fmul(&b, ndc_point, scale), offset);
/* gl_Position will be written out in screenspace xyz, with w set to
* the reciprocal we computed earlier. The transformed w component is
* then used for perspective-correct varying interpolation. The
* transformed w component must preserve its original sign; this is
* used in depth clipping computations
*/
nir_ssa_def *screen_space = nir_vec4(&b,
nir_channel(&b, screen, 0),
nir_channel(&b, screen, 1),
nir_channel(&b, screen, 2),
w_recip);
nir_instr_rewrite_src(instr, &intr->src[1],
nir_src_for_ssa(screen_space));
}
}
nir_metadata_preserve(func->impl, nir_metadata_block_index |
nir_metadata_dominance);
}
}
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